The present invention relates to a method and an apparatus for turning polychlorinated biphenyl (PCB) to harmless. The term PCB used in the present invention is defined as PCB alone or a liquid such as oil, solvent, etc. which contains PCB.
Polychlorinated biphenyl (PCB) is physically and chemically stable and has high heat-resistant and electric insulating property. In this respect, it has been widely used as a product for industrial applications such as insulating oil for electrical equipment and devices, heat medium, lubricant, ink, etc. either by itself alone or by mixing with mineral oil or insulating oil. However, it has been recently discovered that these substances containing PCB are harmful to human being and are environment-polluting and difficult to decompose in the nature, and the production of PCB was stopped. As a result, PCB-containing substances already used have been collected to avoid the possibility of risk and pollution, and PCB-containing products should be kept in storage and processed in order to make them harmless. In the past, efforts for research and development have been made to process PCB and to turn it to harmless substance by methods such as chemical processing, processing by high temperature combustion, processing using metal sodium, etc. All of these processing methods have problems such as high cost for facilities and processing, difficulty in processing of toxic gas, etc. None of these methods is used yet for practical application in the whole world, and waste materials containing PCB are stored in containers and kept in storage without being processed at present.
For example, it is proposed in JP-A-7-241352 that PCB is charged into a melting furnace used for metal refining and kept at temperature of 1100.degree. C. or higher and PCB is thermally decomposed. However, PCB is chemically stable and incombustible, and if it is forcibly decomposed by heating, highly toxic harmful substances of chlorine type or sulfide type are generated. This results in vast amount of cost for waste gas processing Thus, it is practically impossible to process PCB by high temperature combustion method.
To solve the above problems, it is an object of the present invention to provide a method and an apparatus for turning polychlorinated biphenyl to harmless in order to process it at lower cost for facilities and processing and to reduce generation of harmful substances to practically harmless level.
To attain the above object, the method for turning polychlorinated biphenyl to harmless according to the present invention comprises the steps of mixing and emulsifying a polychlorinated biphenyl solution with alumina oxide and silicon dioxide in an ultrasonic emulsifier, charging the emulsified emulsion mixture into an electric resistance type melting furnace, and melting at temperature of 1500.degree. C.-2000.degree. C. and processing to glassy state. The present inventors have found through experiments that the mixture of polychlorinated biphenyl solution and alumina oxide and silicon dioxide are emulsified using ultrasonic energy and can be turned to a type of clay-like substance, and also found that this can be accomplished by melting the mixture in an electric resistance type melting furnace.
Also, the apparatus for turning polychlorinated biphenyl to harmless according to the present invention comprises a storage tank 1 for polychlorinated biphenyl solution connected to an ultrasonic emulsifier 2, a storage tank 4 for alumina oxide and silicon dioxide connected to the ultrasonic emulsifier via a rotary kiln 3, an electric resistance type melting furnace 5 connected to the ultrasonic emulsifier via a monitor unit 8 and an electric resistance measuring unit 9, a feedback piping 22 for feeding back the emulsified mixture obtained from the ultrasonic emulsifier to the ultrasonic emulsifier, and an automatic control unit 10 for measuring emulsified state of the emulsion mixture by said electric resistance measuring unit and for feeding back the incompletely emulsified mixture to the ultrasonic emulsifier via the feedback piping. The reference numerals used for the components in the above arrangement are used simply to provide convenience when referring to the drawings and to facilitate the understanding of the present invention, and the spirit and the scope of the present invention are not limited in any way by these reference numerals.